Magnetic nerve stimulator

• US 5,066,272 A
• Filed: 06/29/1990
• Issued: 11/19/1991
• Est. Priority Date: 06/29/1990
• Status: Expired due to Fees

• Current Assignee: Johns Hopkins University
• Original Assignee: Johns Hopkins University
• Inventors: Fisher, Robert S., Eaton, Harry A. C.
• Primary Examiner(s): Jaworski, Francis
• Assistant Examiner(s): MANUEL, GEORGE C
• Application Number:
  US07/545,801
• Time in Patent Office: 508 Days
• Field of Search: 600/9, 600/13, 600/14, 128/421, 128/422, 128/419 F
• US Class Current: 600/9
• CPC Class Codes: A61N 2/006 for magnetic stimulation of nerve tissue
• CPC Class Codes: A61N 2/02 using magnetic fields produced by coils, including single turn loops or electromagnets A61N2/12 takes precedence

Abstract

A magnetic nerve stimulator comprises a capacitor which is charged to a high voltage, then discharged through a coil placed near the head. The magnetic field produced induces eddy currents in the brain that stimulate neurons. When the capacitor is fully discharged, the discharge path is broken by opening a switch. The inductive action of the coil forces a diode to turn on and the energy from the collapsing magnetic field around the coil charges a second capacitor. The charge on the second capacitor is augmented by a power source to make up for any losses, and the process is repeated. The stimulator of the invention can pulse rapidly, does not cause excessive heating of the coil, and uses comparatively little energy. As a result, high level cognitive functions in the brain can be disrupted for diagnostic purposes.

Claims

1. A magnetic nerve stimulator comprising:

power supplying means for supplying electric charge;

at least two capacitor means connected to said power supplying means for accumulation said electric charge from said power supplying means;

a coil connected to said capacitor means, said coil producing a magnetic pulse when one of said capacitor means discharges said electric charge through said coil and said coil forcing an electric current induced by the magnetic field energy from said coil to charge another of said capacitor means; and

at least two switching means for connecting and disconnecting said capacitor means to said coil to permit the charging and discharging of each of said capacitor means by turns.

2. The stimulator as recited in claim 1, further comprising at least two diode means connected between said coil and said capacitor means, said diode means being turned on by an inductive action from said coil forcing an electric current induced by the magnetic field energy from said coil to charge said capacitor means.

3. The stimulator as recited in claim 1, wherein said stimulator produces a rapid train of large amplitude, short duration magnetic pulses, said train of pulses being sufficient to cause disruption of high level cognitive function in a human brain.

4. The stimulator as recited in claims 1, 2 or 3, wherein said power supplying means comprises a switch mode power supply.

5. The stimulator as recited in claims 1, 2 or 3, further comprising a relay means connected to said coil to reverse said coil'"'"'s connections between said magnetic pulses to prevent the direction of said magnetic field energy from reversing with each of said pulses.

6. The stimulator as recited in claim 5, wherein said relay means comprises a solid state switch.

7. The stimulator as recited in claims 1, 2 or 3, wherein said switching means comprise solid state gate turn-off thyristors.

8. The stimulator as recited in claim 7, wherein said thyristors are connected in parallel.

9. The stimulator as recited in claim 1, 2 or 3, wherein a sum of resistance in said coil, said capacitor means, said switching means, and a cable connecting said coil, said capacitor means, and said switching means is minimized.

10. A magnetic nerve stimulator comprising:

power supplying means for supplying electric charge;

at least two capacitor means connected to sad power supplying means for accumulating said electric charge from said power supplying means;

a coil connected to said capacitor means, said coil producing a magnetic pulse when one of said capacitor means discharges said electric charge through said coil;

at least two switching means for alternately connecting and disconnecting said capacitor means to said coil;

at least two diode means connected between said coil and said capacitor means, said diode means being turned on by an inductive action from said coil forcing an electric current induced by the magnetic field energy from said coil to charge said capacitor means; and

a relay means connected to said coil to reverse said coil'"'"'s connections between said magnetic pulses to prevent the direction of said magnetic field energy from reversing with each of said pulses;

wherein a sum of resistance in said coil, said capacitor means, said switching means, and a cable connecting said coil, said capacitor means, and said switching means is minimized.

11. The stimulator ar recited in claim 10, wherein said stimulator produces a rapid train of large amplitude, short duration magnetic pulses, said train of pulses being sufficient to cause disruption of high level cognitive function in a human brain.

12. A circuit for producing a rapid train of large amplitude, short duration magnetic pulses comprising:

power supplying means for supplying electric charge;

at least two capacitor mans connected to said power supplying means for accumulating said electric charge from said power supplying means;

a coil connected to said capacitor means, said coil producing a magnetic pulse when one of said capacitor means discharges said electric charge through said coil and said coil forcing an electric current induced by the magnetic field energy from said coil to charge another of said capacitor means; and

at least two switching means for connecting and disconnecting said capacitor means to said coil to permit the charging and discharging of each of said capacitor means by turns.

13. The circuit as recited in claim 12, further comprising at least two diode means connected between said coil and said capacitor means, said diode means being turned on by an inductive action from said coil forcing an electric current induced by the magnetic field energy from said coil to charge said capacitor means.

14. A method for magnetically stimulating nerves comprising the steps of:

initially charging a first capacitor means with an electric charge;

discharging said first capacitor means through a coil by closing a first switching means thereby inducing a magnetic pulse;

disconnecting said first capacitor means from said coil by opening said first switching means;

charging a second capacitor means using said coil'"'"'s magnetic field energy;

discharging said second capacitor means through said coil by closing a second switching means;

disconnecting said second capacitor means from said coil by opening said second switching means;

charging said first capacitor means using said coil'"'"'s magnetic field energy; and

repeating said discharging, disconnecting, and charging steps alternating between said first and said second capacitor means.

15. The method as recited in claim 14, further comprising the step of producing a rapid train of large amplitude, short duration magnetic pulses, said train of pulses being sufficient to cause disruption of high level cognitive function in a human brain.

16. The method as recited in claims 14 or 15, further comprising the step of supplying additional electric charge form a power supplying means to each of said first and said second capacitor means after each of said charging steps to fully charge each of said first and second capacitor means.

17. The method as recited in claim 16, wherein said power supplying means comprises a switch mode power supply.

18. The method as recited in claim 16, further comprising the step of minimizing a sum of resistance in said coil, said capacitor means, said switching means, and a cable connecting said coil, said capacitor means, and said switching means to maximize recapture of said coil'"'"'s magnetic field energy.

19. The method as recited in claim 18, further comprising the step of reversing said coil'"'"'s connections between said magnetic pulses to prevent the direction of said magnetic field energy from reversing with each of said pulses.

20. The method as recited in claim 19, wherein said first and said second switching means comprise solid state gate turnoff thyristors.

21. The method ass recited in claim 20, wherein said thyristors are connected in parallel.

22. The method as recited in claims 14 or 15, wherein said charging steps each comprises the step of turning on a first or second diode means using an inductive action from said coil to force an electric current to flow into said first or said second capacitor means, respectively.

23. The method as recited in claim 22, further comprising the step of delaying each of said disconnecting steps until said first or said second diode means has turned on to lower said electric current that must be turned off by said first or said second switching means.

24. The method as recited in claims 14 or 15, wherein said step of charging a second capacitor means comprises the steps of:

closing said second switching means simultaneously with the opening of said first switching means to permit an electric current induced by the magnetic field energy from said coil to charge said second capacitor means; and

opening said second switching means before said second capacitor means discharges.

25. The method as recited in claim 24, wherein said step of charging said first capacitor means comprises the step of:

closing said first switching means simultaneously with the opening of said second switching means to permit an electric current induced by the magnetic field energy from said coil to charge said first capacitor means; and

opening said first switching means before said first capacitor means discharges.

26. A method for magnetically stimulating nerves comprising the steps of:

initially charging a first capacitor means with an electric charge;

discharging said first capacitor means through a coil by closing a first switching means thereby inducing a magnetic pulse;

disconnecting said first capacitor means form said coil by opening said first switching means;

turning on a second diode means using an inductive action from said coil to force an electric current to flow into a second capacitor means to charge said second capacitor means;

supplying additional electric charge from a power supplying means to said second capacitor means to fully charge said second capacitor means;

revering said coil'"'"'s connections;

discharging said second capacitor means through said coil by closing a second switching means;

disconnecting said second capacitor means from said coil by opening said second switching means;

turning on a first diode means using an inductive action from said coil to force an electric current to flow into said first capacitor means to charge said first capacitor means;

supplying additional electric charge from said power supplying means to said first capacitor means to fully charge said first capacitor means;

reversing said coil'"'"'s connections;

repeating said discharging, disconnecting, turning on, supplying, and reversing steps alternating between said first and said second capacitor means; and

producing a rapid train of large amplitude, short duration magnetic pulses, said train of pulses being sufficient to cause disruption of high level cognitive function in a human brain;

wherein a sum of resistance in said coil, said capacitor means, said switching means, and a cable connecting said coil, said capacitor means, and said switching means is minimized to maximize recapture of said coil'"'"'s magnetic field energy.

27. A method for producing a rapid train of large amplitude, short duration magnetic pulses comprising the steps of:

initially charging a first capacitor means with an electric charge;

discharging said first capacitor means through a coil by closing a first switching means thereby inducing a magnetic pulse;

disconnecting said first capacitor means from said coil by opening said first switching means;

charging a second capacitor means using said coil'"'"'s magnetic field energy;

discharging said second capacitor means through said coil by closing a second switching means;

disconnecting said second capacitor means from said coil by opening said second switching means;

charging said first capacitor means using said coil'"'"'s magnetic field energy; and

repeating said discharging, disconnecting, and charging steps alternating between said first and said second capacitor means.

28. The method as recited in claim 27, further comprising the step of supplying additional electric charge from a power supplying means to each of said first and said second capacitor means after each of said charging steps to fully charge each of said first and said second capacitor means.

29. A method for producing a rapid train of large amplitude, short duration magnetic pulses comprising the steps of:

initially charging a first capacitor means with an electric charge;

discharging said first capacitor means through a coil by closing a first switching means thereby inducing a magnetic pulse;

disconnecting said first capacitor means from said coil by opening said first switching means;

turning on a second diode means using an inductive action from said coil to force an electric current to flow into a second capacitor means to charge said second capacitor means;

supplying additional electric charge from a power supplying means to sad second capacitor means to fully charge said second capacitor means;

reversing said coil'"'"'s connections;

discharging said second capacitor means through said coil by closing a second switching means;

disconnecting said second capacitor means from said coil by opening said second switching means;

turning on a first diode means using an inductive action from said coil to force an electric current to flow into said first capacitor means to charge said first capacitor means;

supplying additional electric charge from said power supplying means to said first capacitor means to fully charge said first capacitor means;

reversing said coil'"'"'s connections, and

repeating said discharging, disconnecting, turning on, supplying, and reversing steps alternating between said first and said second capacitor means;

wherein a sum of resistance in said coil, said capacitor means, said switching means, and a cable connecting said coil, said capacitor means, and said switching means is minimized to maximize recapture of said coil'"'"'s magnetic field energy.